Systems and methods are disclosed which are directed to intracranial access for diagnostic as well as therapeutic indications, specifically, an access system, a ventricular catheter, a bolt insert assembly with a probe guide and an introducer.
Access System: Drilling a Hole.
Twist drill devices presently used to drill a hole in the skull have two shortcomings. One shortcoming is an inability to stop drilling as soon as the drill bit has passed through the skull. A second shortcoming relates to the process of removing the bone material generated by drilling a hole. The bone material must be carefully removed from the drill site around the drill hole in a manner that minimizes the material that falls back in the drill hole. It is important that the drill bit is stopped immediately after the drill bit passes through the skull. Any significant movement of the drill bit beyond the skull will traumatize the brain. Currently, a hand drill is used to drill a hole in the skull. A drill stop is placed on the bit to act as a safety device. It prevents the forward movement of the bit beyond a defined point and thereby prevents the drill bit from inadvertently plunging into the brain as a result of continuing pressure on the drill after the hole is completed. The drill stop cannot be precisely located on the bit in a manner that causes the drill to stop forward motion as soon as it passes through the skull. The inability to precisely place the drill stop relates in part to the fact that the surgeon does not know the exact thickness of the skull. The drill stop allows the surgeons to partially drill through the skull without risk of plunging. When the hole is nearly complete, the drill stop is loosened and backed off to allow additional forward movement so the bit can pass through the skull. The surgeon continues to drill very carefully until he senses that the tip of the drill bit has passed through the bone. The sense of when the bit has passed through the skull is not precise and therefore, the distance the drill bit moves beyond the bottom of the skull is not precise. Consequently, the drill bit may move more deeply into the brain than desired. The present invention provides a device that stops the drill bit as soon as it exits the skull and does so in a manner that requires no specialized skill on the part of the doctor.
Access System: Removing Bone Material Generated by Drilling.
A second problem in current methods used to drill a hole in the skull relates to the removal of the bone material that accumulates around the drill bit. The bone material removed from the drill hole forms a sizable anthill-like pile adjacent to the hole. At the end of the drilling process, the doctor removes much of the bone material with a gauze cloth and then removes the remaining material by rinsing the surrounding area. Some of the bone material is flushed into the drill hole in this process. The present invention collects bone material as it is produced, thus preventing an accumulation of bone material around the drill hole. Removing the bone material as it is produced eliminates the need to swab and rinse the drill site.
Access System: Targeting a Ventricle.
Once the hole is created, the surgeon typically attempts to insert a ventricular catheter through the hole and into a ventricle of the brain. The anatomy of the skull and brain is such that an imaginary line perpendicular to the skull at the point of a drill hole will pass through a ventricle. The surgeon aims the catheter at the ventricle by orienting the catheter as best he can so it enters the drill hole perpendicular to the skull. If the catheter is not properly orientated, the catheter will miss the ventricle and require that the surgeon withdraw the catheter and try again. Several prior art devices have been described that direct the angle of entry of the drill bit and or the catheter. The devices are cumbersome enough that they have not been widely adopted. The present invention presents a device that directs the angle of entry of the catheter and does so in a simple-to-use manner.
Therapy: A Catheter with a Standard Drainage Capability.
One important aspect of any ventricular catheter is that of providing a multiplicity of radial holes that lead to a drainage lumen. Multiple holes reduce the likelihood that brain tissue or blood clots will block the flow of cerebral spinal fluid (CSF) into the drainage lumen. Prior art air-column ventricular catheters are constrained in the number of radial holes that can be offered. Generically, an air-column catheter consists of a flaccid bladder mounted to a catheter wherein an air column extends from the bladder to an external transducer. The bladder volume responds to changing ICP according to P1V1=P2V2. The bladder used by the prior art air-column is an external sleeve, which is essentially a tube with its ends bonded to the catheter body. The tube-shaped bladder covers the catheter body beneath it. The bladder length required by the system for proper operation is such that the bladder covers most of the catheter body that resides in a ventricle. The room available for the placement of radial drainage is therefore very limited. The predicate air-column catheter presents 4 radial holes vs. the 10-to 15 radial holes provided in a standard ventricular catheter. An air-column catheter with a sleeve bladder, therefore, has an inferior drainage capability compared to a standard ventricular catheter now used.
In the present invention, the bladder is mounted within the catheter. By placing the bladder within the catheter, the entire surface of the catheter body in the ventricle is available to provide radial hole access to the main drainage lumen and thereby provide the same drainage capability as a standard catheter.
Therapy Access: Placement of Monitoring Probes and a Drainage Catheter Through One Drill Hole.
In the course of managing patients, some neurosurgeons find it helpful to measure parameters such as tissue oxygen. A three-parameter device is presently available that provides access for ICP, O2 and temperature probes. The device does not include the ability to drain CSF. Removing CSF is an important therapeutic procedure in that it provides additional volume within the skull into which traumatized brain can expand. At this time, a first hole is drilled into the skull for placement of the three-parameter device. A second hole is then drilled in the skull to provide access for a ventricular catheter. It is highly desirable to provide a single-hole system that can provide access for multiple monitoring probes such as ICP, oxygen and temperature and also provide access for a ventricular catheter. Such a system would avoid the need to drill a second hole.
Oxygen probes have a very specific placement requirement. They must be placed in undisturbed tissue to obtain accurate values. In the prior art, the ICP, O2 and temperature sensors are placed straight down into the brain through three parallel guide tubes. The oxygen probe is isolated from tissue disturbed by the other two probes by placing the oxygen probe deeper into the brain than the other sensors. Since a ventricular catheter extends all the way through the brain to a ventricle, a system that contemplates the placement of a ventricular catheter and oxygen probe through the same drill hole must cause the oxygen probe to move laterally away from the track of the ventricular catheter. As will be disclosed, the present invention provides an element within a bolt that moves a probe laterally away from the track of the ventricular catheter. Probes vary in their diameter and physical properties and may not interact well with an element designed to move the probe to one side. The present invention uses an introducer with well-defined pushability and memory characteristics to carry a probe into the brain, thus ensuring that all probes can successfully be moved into undisturbed brain tissue.
The introducer can be laterally displaced by placing a deflector at the distal end of the guide tube. It can also be displaced by use of a precurved introducer. Upon exiting a guide tube, the memory of the precurved introducer causes the introducer to move away from the guide tube in an arc. A system that could place four functions, namely, O2, temperature, ICP and a drainage catheter, through a single skull hole would address a clear clinical need by avoiding the need to drill a second hole. The present invention allows all four functions to be placed in the brain through one drill hole.
Adding a Third Parameter.
At this time, neurosurgeons are considering the use of other probes to properly manage the patient. Flow probes, for example, are currently being used to track changes in blood flow rates. In order to enable the disclosed system to accept an additional probe without changing the diameter of the hole drilled in the skull, the oxygen probe is placed in an introducer that has an integrated temperature sensor. Temperature is a necessary input into the oxygen instrument since the oxygen value must be interpreted as a function of temperature. Combining oxygen and temperature into an introducer frees one probe port for use by another parameter such as flow and does so without increasing the size of the bolt and its companion drill hole.